Question: Simplify the following expression: $k = \dfrac{z}{10} - \dfrac{8z}{7}$
Solution: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10$ and $7$ $\lcm(10, 7) = 70$ $ k = \dfrac{7}{7} \cdot \dfrac{z}{10} - \dfrac{10}{10} \cdot \dfrac{8z}{7} $ $k = \dfrac{7z}{70} - \dfrac{80z}{70}$ $k = \dfrac{7z -80z}{70}$ $k = \dfrac{-73z}{70}$